Exxon has taken an unreasonable approach to climate change, but now a multi-part investigation from Pulitzer Prize-winning InsideClimate News has revealed how Exxon's own research confirmed the link between fossil fuels and climate change way back in the 1970s.

The investigation also showed that after some years the company shifted its prime focus to promote and block an international agreement to address the issue.

According to InsideClimate, executives with the company in 1970s heard from a company scientists that carbon dioxide released by burning fossil fuel could lead to warming up of the planet to a catastrophic degree.

The statement given by a company scientist even prompted the company to invest into cutting edge carbon dioxide research throughout the 1980s.

"Present thinking holds that man has a time window of five to ten years before the need for hard decisions regarding changes in energy strategies might become critical", wrote Exxon senior scientist James Black in 1978.

Alter in 1982, Edward David, Exxon's head of research, said that according to some people the world has entered an energy transition away from dependence upon fossil fuels and toward some mix of renewable resources that will not pose problems of CO2 accumulation. The company further shifted its policy in 1980s and 1990s.

Exxon CEO Lee Raymond said in a speech before the World Petroleum Congress in Beijing in October 1997 that they should agree that they really do not know anything about how climate will change in the 21st century and beyond.

Exxon told InsideClimate that its research has always been firmly within the mainstream of the consensus scientific opinion of the day. The company said its work has been guided by an overarching principle to follow where the science leads.